In some applications that the frequency of the sinusoidal wave needs to be adjusted, adjustability for the frequency is demanding. For example, adjustment of the resonant frequency of the gyroscope sensor of PZT architecture. Adjustability for the frequency thereof reaches below 0.1 Hz. DDS (Direct Digital Synthesizer) provides a method of accurately controlling the sinusoidal frequency in a digital manner.
The working principle of DDS is that based on the characteristic that the sinusoidal wave circulates once in every 2π phase angle, the 0˜2π phase is evenly divided into 2N units by using the phase accumulation module (N-bit), and then according to different requirements for frequency, an angle of frequency word is added into the phase accumulation module at regular intervals. The signal amplitude can be obtained by the sinusoidal lookup table from the phase angle output by the phase accumulation module, and output the sinusoidal wave by the digital-to-analog conversion, wherein the overflow of the phase accumulation module represents a circulation of a 2π phase angle.
For an adjustment in which a frequency word is M, after processing of the N-bit phase accumulation module, the resulting frequency fo of the sinusoidal wave of DDS and the working fundamental frequency have the following relationship:fo=(M×fc)/2N 
When 2N/M is an integral, the phase truncation will not occur in this adjustment, but in other cases more or less errors will occur due to the phase truncation. Therefore, the frequency accuracy that the conventional DDS can actually output is very limited, and then the application range is also limited.
On the other hand, as described above, generation of the amplitude of the target signal is implemented by the sinusoidal lookup table. On the basis of the conventional DDS, the bit number of the phase can be cut by reducing the phase accumulation and increasing size of the sinusoidal lookup table, and then phase cut error can be reduced. However, depth of the sinusoidal lookup table and the address size has an exponential relation, so a huge sinusoidal lookup table cannot be built in a reasonable cost to reduce the phase error.